The World Health Organization (WHO) said on Wednesday that it had registered a new daily record number of COVID-19 cases. More worryingly, total infections passed the "tragic milestone" of 5 million on Thursday.

The UN agency's chief Tedros Adhanom Ghebreyesus said that on Tuesday, there were "106,000 cases reported to WHO - the most in a single day since the outbreak began" in December.

The WHO was also getting to grips with US President Donald Trump's reform ultimatum, giving the organization 30 days to overhaul its operations otherwise its biggest contributor would freeze its funding and consider pulling out altogether.

The Geneva-based WHO's coronavirus disease dashboard said that on Tuesday, more than 106,000 confirmed cases had been reported to the agency from around the world.

The new figures come after states around the world have been dramatically ramping up their testing programs.

And the pandemic is still unfolding.

"We still have a long way to go in this pandemic," Tedros told a virtual press conference as his agency warned of rising infection figures in poorer countries.

More than 5 million cases of the novel coronavirus have been registered in total, according to a tally from official sources compiled by AFP.

WHO emergencies director Michael Ryan said the 5 million case mark would be a "tragic milestone."

Tedros added: "We're very concerned about the rising numbers of cases in low- and middle-income countries."

More than 325,000 people have lost their lives, according to the AFP tally.

The WHO's annual gathering of member states agreed Tuesday to an independent probe into the UN agency's coronavirus response.

Trump made public later Tuesday a letter he sent to Tedros, saying that if the WHO did not commit to "major substantive improvements" within 30 days, he would permanently freeze funding to the organization and reconsider US membership.

The US is the biggest contributor to the WHO's budget and has already suspended funding. Pressed on the ultimatum, Tedros said only: "We have received the letter and we are looking into it."

The WHO agreed that an "impartial, independent and comprehensive evaluation" of "the actions of WHO and their timelines pertaining to the COVID-19 pandemic" should be conducted at the "earliest possible moment."

Asked Wednesday when that might be, Tedros said: "When all the conditions we need are actually met."

Trump on Monday made the surprise announcement that he is taking hydroxychloroquine, an anti-malaria drug that his own government experts said is not suitable for fighting the coronavirus pandemic.